In this re-submission of the R03 application we propose to determine feasibility, acceptability, and preliminary effect sizes of a peer-support group alone and combined with group-based financial incentives to increase breastfeeding (BF) duration among low-income Puerto Rican mothers. These interventions will be tested in a Women, Infants, and Children (WIC) program, which capitalize on the current goals of WIC and on the current practice of using incentives to support BF - factors that are likely to increase potential for sustainability and dissemination of the intervention. The study is important because: 1) peer support for BF is the only BF maintenance strategy out of 10 recommended steps to support BF by the World Health Organization (WHO) and the United Nations Children's Fund (UNICEF) for prolonging BF; 2) the proposed interventions have potential to address health disparities related to insufficient durations of breastfeeding, which are particularly prevalent among low-income Puerto Rican women; 3) insufficient breastfeeding is related to multiple maternal and child health problems; and 4) increases in breastfeeding duration could save tens of billions of dollars in health costs. We will follow a three phase strategy. During the Formative Phase we will consult WIC staff, Puerto Rican postpartum mothers, and experts in BF, behavioral health incentives, and WIC populations and settings to develop intervention and research manuals. During the Implementation Phase, we will pilot the interventions and research procedures. We will randomly assign 60 Puerto Rican women who initiate BF to: Treatment-as-Usual (TAU); TAU plus a breastfeeding peer-support group (BFS); or TAU and BFS with group- based financial incentives (also known as Group Contingency Management; (GCM). Participants in the peer- support groups will be encouraged to talk about their BF experiences and problem-solve BF issues. Participants also receiving GCM will be divided into two teams within their peer-support group and each week the team with the greatest proportion of BF mothers (as determined by direct observation of BF) will earn cash incentives in the amount of $5 per team member. We will conduct assessments at baseline, 1, 3, 6, and 12 months postpartum, measuring BF duration, BF exclusivity, BF self-efficacy, and infant weight gain. In the Evaluative Phase, we will examine monthly recruitment, consent, and enrollment rates, as well as attendance and retention rates for the interventions and for research participation (i.e., feasibility and acceptability). We also will estimate effect sizes for BF duraion, BF exclusivity, BF self-efficacy, and infant weight comparing the two interventions to TAU and each other. With WIC programs located in every state, territory, and tribal organization there is increased potential for developing a cost-effective, widely implemented, and sustainable BF intervention.